ABS Caliper Modifications & Brake fluid distribution Question

[JGK95]

In considering a car to buy is Gen II preferabley for mostly track use, I've a couple questions.

If I am attempting to upgrade the Braking System on a Cast Piston Car with ABS:

What modifications will be required to be made to the Master Cylinder if I consider replacing the rear calipers with a set of front calipers which have much bigger pistons and Swept Area?

I have heard of people using the Front Calipers in back and putting a new set of Brembros up front, but what about ABS cars?

What modifications will be necessary to keep the brake fluid's volumetric pressure intact? or possibley increased?

Thanks for All and Any supporting Answers!



Jay K.

 

[Tom F&L GoR]

You can start by calculating a few things. I only have Gen 1 figures, so substitute Gen 2 if you have them. I know the ABS rear calipers are 43mm diameter, front calipers are the same, but don't know about the Gen 2 master cylinder.

Gen 1 master cylinder bore is 27mm diameter, so the area is (pi)(radius)^2, or 3.14*(27/2)^2 = 573mm^2.

There are four 42mm pistons, four 38mm pistons, and two 36mm pistons that will push the pads onto rotors. Assume they all travel the same distance to do so.

The sum of all the areas of the brake pistons comes to 12,114mm^2.

For every mm the pistons move, the master cylinder moves

12114/573 = 21.16 mm

The pedal ratio is 3.48:1, so to move each piston 1mm, and the MC by 21.16mm, the pedal (your foot) will move

21.16*3.48 = 73.63mm, or about 2.90"

(For reference, the stroke on a Gen 1 MC is only 32.17mm.)

The example of putting the front brakes on the back will be disastrous, since the OEM ABS front to rear ratio of piston diameters (and consequently clamping force) is about 78%-22% and you would be going to 50%-50%. I don't know if the ABS can save you, but you would have tremendously oversized rear brakes.

If you put larger front calipers on the front, you can again get close to the original front to rear balance, and let the ABS do the fine tuning (although too large a rear brake may make the car behave funny until a wheel started slipping and the ABS took over.)

In any case, once you knew what the total piston size of your new 6 piston fronts / 4 piston rear set up was, and how much larger than OEM it was, you'd have an idea of how much larger the new master cylinder would have to be to have similar pedal travel.

As far as the ABS goes, I have basically tried to egg on you smarter guys by rambling on above to get an opinion also. I know enough about ABS to understand it cuts brake line pressure, but when the caliper is significantly larger, is the effect on preventing lockup the same, more, or less?

 

[JGK95]

Qoute: Tom:

"If you put larger front calipers on the front, you can again get close to the original front to rear balance, and let the ABS do the fine tuning (although too large a rear brake may make the car behave funny until a wheel started slipping and the ABS took over.) "


Tom,

WOW!!

Thanks for the Response! When I get the car the first goal was to immediately replace the rear calipers with the Fronts and get bigger front calipers. Your response has educated me and is greatly appreciated! I got my work cut out for me, thats for sure!

Thanks again,

Jay K.

ps. Is it strange that my first desired mod isn't under the hood

 

[Bugeater]

JGK95,
You may want to look into putting the SRT-10 setup on the GENII. Its been done (even adding ABS to non-ABS cars) but not alot of feedback yet. Waiting to hear some comparisons to Stock, GENIII, Stoptech etc...

Valaya racing does it in-house, and also sells the parts.